pwm.ino

// the number of the LED pin
const int ledPin = 15;  // 16 corresponds to GPIO16

// setting PWM properties
const int freq = 5000;
const int ledChannel = 0;
const int resolution = 8;
 
void setup(){
  // configure LED PWM functionalitites
  ledcSetup(ledChannel, freq, resolution);
  
  // attach the channel to the GPIO to be controlled
  ledcAttachPin(ledPin, ledChannel);
}
 
void loop(){
  // increase the LED brightness
  for(int dutyCycle = 0; dutyCycle <= 255; dutyCycle++){   
    // changing the LED brightness with PWM
    ledcWrite(ledChannel, dutyCycle);
    delay(15);
  }

  // decrease the LED brightness
  for(int dutyCycle = 255; dutyCycle >= 0; dutyCycle--){
    // changing the LED brightness with PWM
    ledcWrite(ledChannel, dutyCycle);   
    delay(15);
  }
}

pwmBaseRead.ino

const int ledPin = 15;
const int freq = 5000;
const int ledChannel = 0;
const int resolution = 12;

void setup() {
  // put your setup code here, to run once:
  pinMode(26, INPUT);
  Serial.begin(115200);
  ledcSetup(ledChannel, freq, resolution);
  ledcAttachPin(ledPin, ledChannel);
}

void loop() {
  int val = analogRead(26);
  val = map(val, 0, 4096, 0, 255);
  Serial.println(val);
  ledcWrite(ledChannel, val);  
}

Link RTC library : https://github.com/adafruit/RTClib